Traditional plant breeding to include parental lines for desirable traits involves crossing selected parental lines to introduce those desirable traits into the progeny of the cross. In a crossing-based approach, often, not only the desirable trait is transferred to the progeny but some randomization of the genomes of both parental lines occurs. This results in a wide segregation and variation of morphology and other traits of the progeny, which are not predictable. The uncontrolled variation renders the progeny selection process very long, cumbersome and laborious especially if the desired traits are not expressed early in the progeny or if the desired trait is recessive.
In an effort to minimize the random variation, breeders prefer homozygous parental lines (inbreds) so that the genetic make up of the F1 generation is more predictable. The inbreds with a desirable trait are generated by back-crossing a heterozygote with its parental lines, followed by segregation selection and repeated back-crossing. However, this repeated back-crossing is also very long, usually up to 6 to 7 times, depending on the plant, would produce a homozygous plant with the desired trait. Of course, the time scale involved here is dictated by the rate at which plants grow to maturity and set seed and several years can be necessary to produce the desired homozygous parent line.
Haploid plants contain one half of the usual complement of genes. Normal plants are diploid in that they have two complete sets of chromosomes, one from each parent. Polyploid plants have more than two sets of chromosomes. Haploid plants are capable of growing to maturity but are generally sterile. There are several known methods of generating haploid plants.
One way to obtain homozygous plants without the need to cross two parental lines followed by a long selection of the segregating progeny, and/or multiple back-crossings is to produce haploids and then double the chromosomes to form doubled haploids. The production of doubled haploid plants yields highly uniform inbred lines and is especially desirable as an alternative to sexual inbreeding of longer-generation crops. By producing doubled haploid progeny, the number of possible gene combinations for inherited traits is more manageable. Thus, an efficient doubled haploid technology can significantly reduce the time and the cost of inbred and cultivar development. Chemicals such as colchicines are used as chromosome doubling agents. However, due to their mammalian toxicity and low efficiency, their use in plant breeding has been limited. Therefore, agents to induce chromosome doubling in plants with low mammalian toxicity are desirable.